Tính nhanh :
29,75 x 90,98 x ( 9,5 - \(4\frac{3}{4}\)x 5 ) +1,93 x ( \(1\frac{1}{2}\) + 8,5 )
K
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ND
0
26 tháng 8 2018
a)\(x=\dfrac{-14\cdot52}{72}\\ x=\dfrac{-91}{9}\)
b)\(x=\dfrac{120\cdot7.2}{70}\\ x=\dfrac{432}{35}\)
c)\(x=\dfrac{2\dfrac{2}{3}\cdot8.5}{5}\\ x=\dfrac{68}{15}\)
d)\(x=\dfrac{4\dfrac{2}{5}\cdot9.5}{8}\\ x=\dfrac{209}{40}\)
22 tháng 6 2015
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K
27 tháng 12 2017
quá dễ tách ra thành 1\x-1\x+1+1\x+1-1\x+2+1\x+2-1\x+3+1\x+3-1\x+4+...+1\x+5-1\x+6
=1\x-1\x+6
=6\x(x+6)
KT
27 tháng 12 2017
\(\frac{1}{x\left(x+1\right)}+\frac{1}{\left(x+1\right)\left(x+2\right)}+\frac{1}{\left(x+2\right)\left(x+3\right)}+\frac{1}{\left(x+3\right)\left(x+4\right)}+\frac{1}{\left(x+4\right)\left(x+5\right)}+\frac{1}{\left(x+5\right)\left(x+6\right)}\)\(=\frac{1}{x}-\frac{1}{x+1}+\frac{1}{x+1}-\frac{1}{x+2}+\frac{1}{x+2}-\frac{1}{x+3}+\frac{1}{x+3}-\frac{1}{x+4}+\frac{1}{x+4}-\frac{1}{x+5}+\frac{1}{x+5}-\frac{1}{x+6}\)
\(=\frac{1}{x}-\frac{1}{x+6}\)\(=\frac{6}{x\left(x+6\right)}\)
14 tháng 10 2019
\(9,5-\frac{3}{4}\left|X-\frac{1}{3}\right|=6\frac{1}{3}-\frac{1}{3}\left|\frac{1}{3}-X\right|\)
\(\frac{19}{2}-\frac{3}{4}\left|X-\frac{1}{3}\right|=\frac{19}{3}-\frac{1}{3}\left|X-\frac{1}{3}\right|\)
\(\frac{19}{2}-\frac{3}{4}\left|X-\frac{1}{3}\right|+\frac{1}{3}\left|X-\frac{1}{3}\right|=\frac{19}{3}\)
\(\frac{19}{2}-\left(\frac{3}{4}\left|X-\frac{1}{3}\right|-\frac{1}{3}\left|X-\frac{1}{3}\right|=\frac{19}{3}\right)\)
\(\left|X-\frac{1}{3}\right|\left(\frac{3}{4}-\frac{1}{3}\right)=\frac{19}{2}-\frac{19}{3}\)
\(\frac{5}{12}\left|X-\frac{1}{3}\right|=\frac{19}{6}\)
\(\left|X-\frac{1}{3}\right|=\frac{19}{6}\div\frac{5}{12}\)
\(\left|X-\frac{1}{3}\right|=\frac{38}{5}\)
\(\Rightarrow\orbr{\begin{cases}X-\frac{1}{3}=\frac{38}{5}\\X-\frac{1}{3}=\frac{-38}{5}\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=\frac{119}{15}\\x=\frac{-109}{15}\end{cases}}\)
Vậy.....................
P/s: sai thì bỏ qua nha!
DQ
0
16 tháng 8 2016
\(\frac{1}{1}.\frac{1}{2}+\frac{1}{2}.\frac{1}{3}+\frac{1}{3}.\frac{1}{4}+\frac{1}{4}.\frac{1}{5}+\frac{1}{5}.\frac{1}{6}=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)
\(=1-\frac{1}{6}=\frac{5}{6}\)
16 tháng 8 2016
\(\frac{1}{1}.\frac{1}{2}+\frac{1}{2}.\frac{1}{3}+\frac{1}{3}.\frac{3}{4}+\frac{1}{4}.\frac{1}{5}+\frac{1}{5}.\frac{1}{6}\)
\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}\)
\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)
\(=\frac{1}{1}-\frac{1}{6}\)
\(=\frac{5}{6}\)
S
3 tháng 7 2019
\(17.8+51.4=34.4+51.4=4\left(51+34\right)=4.84=336\) \(2.2.3.5.19=\left(2.5\right).\left(3.19\right).2=10.2.57=570.2=1140\) \(54.275+825.15+275=54.275+45.275+275=275\left(54+45+1\right)=100.275=27500\) \(\frac{167.198+98}{198.168-100}=\frac{167.198+98}{198.167+198-100}=\frac{167.198+98}{167.198+98}=1\)
\(\frac{1}{n}-\frac{1}{n+k}=\frac{k}{n\left(n+k\right)}\Rightarrow\frac{1}{1.2}+\frac{1}{2.3}+.....+\frac{1}{2019.2020}=1-\frac{1}{2}+\frac{1}{2}-....-\frac{1}{2020}=1-\frac{1}{2020}=\frac{2019}{2020}\)
TG
3 tháng 7 2019
a) 17 x 8 + 51 x 4
= 17 x 4 x 2 + 17 x 3 x 4
= 17 x 4 x ( 2 + 3 )
= 14 x 4 x 5
= 14 x 20
= 280
b) 2 x 2 x 3 x 5 x 19
= ( 2 x 5 ) x ( 3 x 19 ) x 2
= 10 x 57 x 2
= 570 x 2
= 1140
c) 54 x 275 + 825 x 15 + 275
= 54 x 275 + 275 x 3 x 15 + 275 x 1
= 54 x 275 + 275 x 45 + 275 x 1
= 275 x ( 54 + 45 + 1 )
= 275 x 100
= 27500
d) 100 - 99 + 98 - 97 + 96 - 95 + 94 - 93 + ... + 4 - 3 + 2
= (100 - 99) + (98 - 97) + (96 - 95) + (94 - 93) + ... + (4 - 3) + 2
= (1 + 1 + ... + 1) + 2
( 49 số 1 )
= 49 + 2
= 51
k) 1,5 + 2,5 + 3,5 + 4,5 + 5,5 + 6,5 + 7,5 + 8,5
= ( 1,5 + 8,5 ) + ( 2,5 + 7,5 ) + ( 3,5 + 6,5 ) + ( 4,5 + 5,5 )
= 10 + 10 + 10 + 10
= 40